Vacuum-tube detector



June 3, 1930. s, QHL I 7 1,760,957

VACUUM TUBE DETECTOR Filed Dec. 9, 1925 INVENTOR W ATTORNEY Patented JuneIp, 19 7 g TynotI UM-TUBE;DETEoTDit- Application filed jl ljec'einher !;119254;;Serial 1To.: 74,3$4.2

Thisinventi'on relates to vacuum tube leak detectors, and more particularly to are rangements for increasmgthe normaloutputof a grid leakvacuum tube detector.

@A vacuum tube ,con's'ists' essentially of avessel containing a thermionic-cathod-e generally in the. form of a filament heatedfby passing a current through it, an anode; and a discharge controlling electrode, generally inthe form of awire 'mesh or grid, which is,

placed between the cathode and the anode. This discharge controlling electrode-may be' of any form because a controlling effect onthe;

. thermionic emission between the cathode and for various applications V frequency amplifiers, it is; frequently the pracp phonereceiver 1'2 and afresistance 13 The the anode can be obt'ainedf by positioning any conductor with respect to *the path so: that potential" variations applied thereto will nt'be cause variationsin'the thel'mioniccur'r tween the cathode and the anode; p f r 7 Vacuum tubes of various types aresdesigned' For use: as high tice to use tubes of low or moderate power out-I put; employing gridand platepotentials'suib ablefor satisfactory operation as distortion less amplifiers-1 Similar'tubes are also used'as grid leakdetectors but when tubes a're so used, the grid potential is ordinarily Z'ero'or positive-with respectto the catho'delfThe plate potentialr is frequently reduced to :half 5 the value employedforamplifier operation inorder to avoid the possibility of 'voltagejsat uration. Such voltage "saturation-mightseriously redufce'the detector 'sensitivity vforwe'ak r signals." This'reducti'onin the platepotential 7 results in a reduction of the energy output obtainable without" di'stortion,-fr om *a tube used as a grid lea-kdetector; as'comparedfwith that obtainable from the same tube used 'asaan amplifier with thesame plate and' gridipoten tials." T Q V It is an object of this invention to. provide an'arrangement for'increasing'the power out putof a vacuum tube detector. r VVh'ile the nature of-[the invention will be pointed out with particularity in the'a' pend ed claims; the inv ntion itselffbothasto' its objects and" features, will "be more i easily'j finf derstood from the detailed" description here inatter followingv when read in connection which are'lto bereceived are selected by fa" tun; 9 v r vacuum tubeincludesthe anode 6; the cathode n hel anode and the cathodeis-thejpoten' due to resistance connected" in{the-'outputi I circuit; LAlso, a small directcurrentordinari a ly flows in the input circuit sinc eithe grid isnormally at a, positive potential with respect ito the negative end of the cathode, which po V tential is a determined }by the. potentialdro'p; across the-cathode minus the potential drop in":

'with tlie acconipanyingdrawing'sliowing Referring to Figure 1, the antenna or re; ceiving c rcuit; consists o'f the antenna 1 and an ndufctance 2 connected to ground. Signalsing circuit including an inductance and a variable condenser There is Shawna-vac;

'uu'rn tube 5' or the three-electrode typefh-aV-Q in'g ananode 6, a cathode 7 an'da 'dischargei contig'oll ngelectrode8. The input'circu-itfor this vacuum tube includes't'he cathode 7 and connected to the tuning circuit includingin-Q,

ductance and the variablecondenser-1 4 through 'a grld condenserfi andfa re ,1 a a sistan'ce leak-'10; 3 The output" circuit" of thief 7 source of electromotive*forfce a telecondenser. 14 shunts the resistance 13 for ,'alternating currentv components of theplate' current. A battery-1'5 is employedforheating' the cathode i oscillations are being receivedby thegrid{ leak? detector; a steady current flo'v'vs in the output circuit, and the potential existing be tial ofithe source minus the dropin-jpotential the' grid leak resistance caused by theiflow 013 1 fgridcurre'nt'therethrough; The'gri'd orjdis-i L I 7 charge control;electrode th en assumes;th p'ia-V r proximatepotential'correspondingto'the part I "of 'theflcathode, whichi thiscircuit as ce When thl antenna circuitbeconies energize'cl"by inccmingoscillations;aiij o'scillatory ff J current is setup in the tuned circuit;and an the discharge controlling electrode 8; ;an d is p '7; orthei-vacuumetube "5 to V icandesce'nce, 1 s 7 7; v 7' In'thecircuit'shown" in Fig lfwhen no; 1

alternately positive and negative electromotive force appears across the terminals of the condenser in the input circuit. This alternately charges the discharge controlling electrode positively and negatively. 'During the part of the cycle in which thedischarge controlling electrode becomes positive, some of the electrons present in the tube are attracted by the discharge controlling electrode.

During that partmof the cycle in which the discharge controlling electrode becomes negautive,none of the electronsare removed from thedischarge controlling electrode, and a negative charge thus builds up thereon. This hasthe effect of accumulating a'negative charge on thedischarge controlling electrode which acts so as todecrease the normal electronic current flowing between the cathode and theanodeh It is therefore necessary to include a high resistance leak in the input circuit so as-to provide a path by which the charge onthe discharge controlling elec- Arrangements which are used trode may leak back to the cathode. This permits the potential of the grid to vary at voice frequencies but not at carrier frequencies be- 7 static characteristic curve, the point atwhich the slope is greatest. V V oIn, fact, rectification actually takes place'. 4e

in the input circuit of agrid leak-vacuum tubejdetector, and the vacuum tube is employed for amplifying the si nals. The variations of the current in the output circuit are greater than'the variations of the current in the input; circuit.

' In order, to increasethe available output of a vacuumtube for an increased current inathe input circuit, itis necessary to increase the potential of the source connected in the output'circuit. In accordance with this invention,--the source of potential 11 is higher than that normally employed in connection witha detector tube, and the resistance 13 is connected in series. with the source of potential llcso as to cut down the potential] impressed between the anode and the cathode ofthe vacuum tube 5 for low input'levels. Whenthe .tube functions as a detector for high input levels, the plate current, which -w ould be normally reduced, does not incur sucha great change byvirtue ofthe ratio that the resistance 13 bears to the resistance in the restof theoutputcircuit. Asspming that R is-the magnitude of the resistance 13 in ohms,

5 that E is the difference of potential existing between the anode and the cathode of the vacuum tube 5 in Volts, that E is the potential of the source of electromotive force 11 in volts, and that I is the current flowing in the output circuit of the vacuum tube 5 in to the electromotive force of the source E An alternating current present in the input circuit produces variations in the current in the output circuit about that part of the static characteristic curve at E When the resistance 13 is present in the output circuit of the vacuum tube 5 and the currentl flows therethrough, then the electromotive force E of the battery 11 equals the potential drop across the resistance 13, RI, plus the potential difierence existing between the anode and the cathode of the vacuum tube 5, E Thus E =RZ+E 1 and therefore,

E being the difference of potential between the anode and cathode of the vacuum tube 5. Also, when the current in the output circuitl increases, the .potentialexisting between the anode and the cathode of the V8.61 uum tube 5, E will decrease, and conversely, when-the current in the output circuit decreases, the potential existing between the anode and the cathode increases.

7 The greater the resistance R included in the output circuit of the vacuum tube, the greater will be the variation in the potential existing between the anode and the cathode of said tube brought about by a variation in the potentialimpressed betweenthe anode and control electrode of the tube. If the re sistance l3 were'of infinite magnitude, and the supply of voltage were also infinite, there would be'no change in the current flowing in the output circuit of the vacuum tube for all valuesof the current flowing in the input circuit of the vacuum tube. V

In this invention, whenthe current flowing in the input circult of the detector increases,

greater current flows in the output circuit of the detector than would otherwise flow in the output circuit of this detector if an ordinary potential were connected therein. The drop in potential is taken up by the resistance 13 when the tube 5 functions as a detector for low input levels. VJ hen thetube functions, as. a detector for high input levels, then the plate current, which would be normally reduced, does not incur a large change due to the presence of'theresistance 13. Any plate voltage may be used with this system providing the magnitude of the resistance is adjusted so that it equals that obtained from the expression (2) above, in which E is the would be had if thetube were used'a's an am- -plifier. i

potential for which' the tube is designed. When the resistance 13 is very large,the level of the detector approaches the level which.

In shown-a modification ofthe arrangements'of Fig. 1, in which thes'ame i the invention and the scope of the appended therethrough. A condenser 16 is connected charge device having an anode, a cathode and reference characters areused as in Fig. 1'to represent the same parts. In this figure the resistance13 is connected in series with-the source of potential 11in the output circuit, I and the condenser 14 is connected across the terminals of the resistance-13 and the source 7 of potential 11, so as to by-pass alternatingf current components of the anode current" across the terminals of the telephone receiver 12 so as to permit low frequency currents to flow'through the telephone receiverilQand the high frequency currents to flow through the condenser 16. The magnitude of the re-. sistance 13 maybe ordinarily determined from the expression (2) given hereinabove, in which E is the potential of the source of electromotiv-e force 11 and E is the'plate fila ment potential 'itor'which the tube is designed.

" While the arrangements of this invention have been disclosed in certain particular "em bodiments which are deemed desirable, it is to be understood'that'it is capable of embodiment in other and widely varied forganiza ti'ons without departing from the spirit of.

claims.

What is claimed is:

1. In a receiving system, a receiving cir-- cuit, a tuned circuit couple'clvthereto,a dis an impedance varying element, said'dischar-ge device being connected to said tuned circuit for the'rectification of incoming oscillations therein, :a telephone. receiver connected tosaid dischargedevice, and means'including put levels.

1 telephone receiver for increasing the "speech a high resistance connected in series with said level for incoming oscillations of higher am plitudes without therebycausing a materialchange inth'e sensitivity of the system, for

incoming oscillations of lower amplitudes.

'2. Asystem comprising a'space discharge: device of the three-electrodetype,circuit arrangements .operatively associated with said device including a grid leak input circuit,

an output circuit, a tuned circuit, and means includinga resistancein said output circuit for obtaining high output levels for high in- 8. Inareceiving system, a receiving circuit, a tuned circuit coupled thereto, a vacuum tube having an anode, a cathode and a control electrode, said vacuum tubebeing cou- I pled to said tuned circuit to permit the rectification of signals therein, a telephone recelver connected to sald vacuum tube, and

1 means includinga high resistance for in-- i I, k in -7 .4. A system comprlsi'ng .avacuum tuba;

circuit arrangements op'eratively associated WltlL sald: vacuumlrtube includ ng a grid leak input circuit, vanu'output circuit, a tuned cirg lcuit, andmeans including a resistance and a source of potentialin-said output circuit forfmakin'g theoutputlevelof the tube ap-- preach the outputflevel o the tube used a's an amplifier, the] potential of said source be,

ing substantially higher than that required r V r a I so I forigood (l6iGClZl1'lg 21Ci3 1011 by the vacuumtube, i v the circuits being so'arranged that the gre at-' er: the magnitude of lthef resistance and the i; greater the potentialof the source, the more nearlythe outp ut levelofthe tube approaches the output levelflof the same tube used'as amplifier irrespectiveof'input levels.

I 5. A grid f leak "detector system includingQa Q three-element vacuum tube,.a high, constant potential platebattery at the vacuumitube,

.andmean'sfto' maketheoutput-level of the.

vacuum tube approach the output level of thei 7. same tube .used' as an i amplifier. V

' 6. In a radio receiv ng c1rcu1t, anantenna circuit, a three-element' yacuum tube, a grid leak input circuit for said tube tuned to said antennacircuitya receiver, an output circuit Yforrsaidtube tuned so that signals are heard in's'aid receiver, and means including a high i resistance in series with said receiver -f0rfl increasing the Vcurreht'inlsai'd' receiver beyond I I the current. normally :fobtainable with c the same tube used as afdet'ector'.

' 7;"Incombination, athree-element vacuum tube, a grid condensefla grid leak,-said grid condenser and leakbemg lncluded in the'i-nput circuitof saidltube', a batteryofhiglier potential than": that normally required for proper actionof the vacuum tubeas a dea I tector, and a resistanceysaid'batteryand said resistance being included in the output circuit'of said tube, the fluctuating direct current in the output circuit increasing as the magnitude of the grld current lncreases.

8 A receiving circuit com'prising a dis rcharge tube of'thethree-electrode type, a.

.grid condenser andlealg said grid condenser and leak being includedin the input circuit '7 of said tube,,abattery,'anda resistance, said-f." l i battery and said resistance being included A in "the output circuit fofsaidtube, the ratio that said resistance bears'to the total resistance of the outputjcircuit alternately increasing and decreasing as the amplitude of the waves impressed on said input circuit decreases and increases.

9. In a radio receiving circuit, an antenna c1rcu1t, a condenser, a grld leak, a vacuum tubehavingan anode, a cathode, and a grid 7 the nput circu1t for saidvacuum'tube ins eluding the cathode and grid of saidvacuum -tube and said condenser andgrid leak, said input" circuit being coupled to said antenna c rcuit, a lngh resistance, a high potential 'battery, the potential of said battery being substantially hi her than that required When the vacuum tube is acting merely as a detector, and a receiver, the output circuit for said vacuum tube "including said resistance, said high potential battery and said receiver.

10. A radio circuit comprising a vacuum tubehaving an anode, cathode and a control electrode, an input circuit including said cathode and said control electrode for the rectification of signals therein, an output circuit including said cathode and said anode which has a high potential source of current for good detecting action and a high resist- 7 December, 1925.

and a resistance therein of such magnitude that theoutput level is at a'maxiinum for all input levels.- 7

11. A detector for signaling systems including a source of potential of a magnitude several times as large as is normally required ance in'series With said source or" potential, said source of potential and said resistance being so related to the detector that detected signals have maximum audibility Without appreciable distortion.

12. A three-electrode vacuum tube system comprising means for increasing the audibility of signals detected thereby by any predetermined amount Without appreciable distortion, said means including in series relationshipa high potential source of plate current of a magnitude substantially greater than that ordinarily required for normal detecting action and ahigh resistance.

In testimony whereof, I have signed my name to this specification this 8th day of RUSSELL S. OHL.

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